Catalytic processes for the treatment of hydrocarbons are well known, particularly hydrogenation treatments such as hydrodesulfurization, hydrotreating, hydrocracking, and the like in a fixed bed reactor. Such processes are multi-phase and require the mixing of gas and liquid streams. Catalytic hydrogenation reactions, for example, are generally exothermic in character, and temperature control of the reactor is an important feature. This is typically addressed in the art by using two or more vertically supported catalyst beds mounted in series in the reaction vessel with the mixed phase fluids flowing downwardly and discharged at the bottom of the vessel. Hydrogen gas is typically used as a quench between beds.
Mixing gases and liquids is a difficult task because the large density difference tends to a quick separation. Good mixing, however, is important to insure a relatively even temperature and/or component composition distribution in the mixture. Heavier and lighter components can channel through the catalyst bed or other vessel internals. In a quench zone, good mixing is also necessary to obtain an effective quench. Otherwise, an uneven temperature distribution in the reactant stream can result in temperature control problems, localized hot spots, and unwanted reaction products in the lower beds, and premature catalyst degradation.
The mixing problem in the quench zone is complicated by the occurrence, at least to some extent, of mixed-phase conditions within the previous catalyst bed and attendant channeling mentioned above. Furthermore, since the amount of quench gas used is relatively low compared to the large quantity of hot effluent fluids and the large cross-section area of the reactor vessel which must be covered, excellent mixing between the effluent fluids and quench gas is important if a sufficient degree of cooling and temperature uniformity is to be achieved.
The art of gas/liquid mixing design has typically been conceptually based on providing a holdup region for the liquid components and a means for sparging the gaseous components into the liquid holdup. In addition, mixers have generally functioned as distributors for enhancing reactant distribution over the cross-section of the reactor beds.
U.S. Pat. No. 3,592,612 to Ballard et al discloses a two-stage mixing device, comprising a horizontal tray adapted for installation in a downflow contacting vessel, a first stage mixing box mounted on an upper surface of the tray, a second stage mixing box attached to an under surface and at least two spaced apertures in the tray communicating the mixing boxes.
U.S. Pat. No. 3,598,541 to Hennemuth et al. discloses an apparatus for contacting two fluids in a fluid-solids contacting zone, wherein a first fluid (e.g. a gas) is passed into a central chamber having a plurality of fluid openings in the chamber wall while a second fluid (e.g. a liquid) is passed into an annular chamber encompassing the central chamber and spaced apart therefrom. The second fluid is discharged via fluid openings in the inner annular chamber wall, into an annular space between the chambers, and the first fluid is discharged from the central chamber into the second fluid discharge. A resulting fluid mixture is passed from the annular space into a bed of particulated contact solids.
U.S. Pat. No. 3,556,736 to Boyd discloses an apparatus for contacting two fluids in a fluid-solids contacting zone, wherein a first fluid (liquid) is passed downwardly into a distributor downcomer and a second fluid (gas) is passed upwardly into the downcomer via an inlet nozzle contained within the downcomer. A resulting mixture passes down through the annulus confined between the downcomer wall and the inlet nozzle and enters the particulated solids below.
U.S. Pat. No. 3,218,249 to Ballard et al. discloses a vapor-liquid feed distribution means in a hydrocarbon conversion process comprising a mounted horizontal tray having cap and downcomer means through which the vapor and liquid feed materials are distributed onto a bed of contact material. An improved means for contacting and distributing vapor-liquid mixed phases is said to be provided.
Additional U.S. patents which may be of interest include U.S. Pat. No. 3,958,952 to van Ginneken and U.S. Pat. No. 3,796,655 to Armstead et al.